What is the appropriate penalty for a player who has an illegal number of cards in their deck?

When a player is found to have an illegal number of cards in their deck, the appropriate penalty is a Game Loss. This is in alignment with the policies set forth in the Magic: The Gathering Judge Infraction Procedure Guide. The rationale behind this penalty is that having an incorrect deck size undermines the integrity of the game, as it affects the player’s ability to engage in fair competition.

A Game Loss serves as a significant consequence because it directly impacts the player's current match, which reflects the seriousness of adhering to deck-building rules. The rules specify that a player must have exactly 60 cards in their main deck for most formats; deviating from this creates an unfair advantage or disadvantage and disrupts the balance of the game.

Other potential penalties, like a Warning, would not sufficiently address the seriousness of this infraction, as it fails to impose a consequence that reflects the impact of the violation on the game state. Similarly, a Disqualification is reserved for more severe infractions or repeated offenses, while Deck modification typically pertains to other situations in which a player may be allowed to modify their deck within certain constraints, rather than dealing with an illegal deck size.